ok, so i have installed 3 PAC brand ground loop isolators (front, rear, sub) and grounded them to the head unit's frame. it took care of 98% of the noises! replacing the alternator capacitor and testing another set of nice rca cables laying over the seats did nothing. this whole thing really bothers me though because i know it was working perfectly and these isolators are a band aid. i would love to solve the issue and remove the isolators at some time. any more thoughts would be much appreciated but i'm glad this sounds good now!

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83 300CD- sanden, dual p/f condensers, 160a alternator, ect
91 300TD- 722.6, #22 head, 3.5L IP, w140 manifolds, ect